Potentiometer



I April 14, 1 942. "H. M. DRESSEL POTENTIOMETER Filed- Nov 14, 1940 "llllllllllrlillll II Patented Apr. 14,1942

POTENTIOMETER Henry M. Dr'essel, Chicago, 11]., assignor to Oak MI Co acorporation o! lllinom Application November 14, 1940, Serial No. 365,665 3 Claims. (0]. 179-10m41i This invention relates to a potentiometer and while of general application is particularly adapted for use where rapid variations in potential are to be produced. In particular this invention is useful for translating sound wavesinto electrical impulses such as in pick-ups for sound reproduction from wax records, microphones,-

rent involved is of the order of several microamperes.

From a commercial angle, it is desirable that i a translating device be simple, easy and cheap to of a device of this character when used for sound reproduction from wax records is important from a practical angle.

. Inasmuch as a pick-up is an inertia device, it

is evident that if the mechanical resistance 01" the movable portion of the pick-up is great then the weight of the entire device must be sufliciently great to permit the pick-up to operate. Such a weight results in a substantial pressure upon the needle point in the record groove and thus makes for rapid wear and breakdown of the record grooves. It is clear therefore that if a light needle pressure is to be used, thenit is necessary to make the movable element of the a translating device connected directly to the grid of a vacuum tube, it would therefore be highly advisable to have the potentiometer electrode operate over a resistance of the order of about two hundred thousand ohms. This may -be larger or smaller under various conditions.

For practical operation of a translating device with an amplifier, it is desirable that the potentiometer varies the potential of the control electrode over a range of about one or two volts. In

other words, therefore, the potentiometercurtiometer.

manufacture, be rugged and have a long useful life. The invention hereinafter disclosed fulfils these requirements to a remarkable degree while satisfying the technical requirements.

In general this invention provides a potentiometer wherein the resistance element is a body of liquid. For stable operation and long life it is highly desirable to prevent electrical decomposition of the liquid by virtue of the passage of current therethrough. This, of course, is true if direct currents are impressed upon the poten In the case'of alternating currents, however, little if any decomposition will result. For use in a phonograph, a potentiometer pickup is preferably connected to a suitable source of direct current, this being readily available. A high frequency alternating current may be used with the record variations being used modulating in the event that alternating currents are desired.

A pair of spaced electrodes are disposed in the liquid and upon these electrodes there is impressed the difference of potential previously referred to. The potentiometer electrode is disposed between said spaced electrodes in said liquid. By moving the potentiometer electrode between said spaced electrodes, the potential of said potentiometer electrode is varied as it travels along the potential gradient between the spaced electrodes.

From a mechanical angle and in order to avoid any fine dimensions and work, it is preferred to space the electrodes a distance apart of the order of about one quarter or one-eighth of an inch. This of course may be greatly varied. Considering the amount of motion of the potentiometer electrode when actuated by a record needle operating in a groove or when actuated by a microphone diaphragm, it will be found that potential variations of the order of about one or two volts are impressed upon the potentiometer eiwtrode when the potential difierenoe between the spaced electrode is about two or three hundred volts with the spacing given above. It is thus evident that for satisfactory operation under the above conditions, liquids having a substantially high resistance must be used.

As a general rule, liquid insulators such as mineral oil in pure form have too high a resistance and are not suitable. Obviously the ordinary electrolytes have too low a resistance.

I have determined that organic liquids having an OH radical may be suitable. Thus the various alcohols have desirable characteristics. These alcohols are preferably used as supplied in commercially pure concentrated form. Thus I have successfully used methyl alcohol, ethyl alcohol, butyl, amyl and other higher alcohols. Mixtures of these alcohols may also be used. Polyhydric alcohols such as ethylene glycol or glycerine may also be used. It is also possible to dissolve some mineral oils in one or more of these alcohols and adjust the resistance characteristics.

It is preferred to use a high boiling liquid so that a device may be sealed without building up excessive vapor pressures under normal room conditions} However, any liquid having a suitable resistance may be used.

It is preferred to have the opposed surface area of the spaced electrodes as small as possible. mum and concentrated. The potentiometer electrode may also have a minimum area transverse to the potential gradients spanning the spaced electrodes. ,While a fine potentiometer electrode may be used, I prefer to use a potentiometer electrode having a substantial area lying in a plane parallel to the line joining the spaced electrodes. In effect such an electrode serves to concentrate practically all of the potential gradients in itself and creates two separate series connected liquid paths. Thus the movement of such an electrode results in a maximumvariation of potential. It is clear that if Thus current flow is reduced to a mini-- carbon. However, I have found that platinum or gold remain clean and I prefer them.

In order to reduce electrode exposure to a minimum, the casing material may be extended asat l9 and 20 inwardly from the wall. The same effect may be obtained by rubber sleeves pulled over the wires. Electrodes l1 and I8 extend through casing wall 55 to form terminals. As is clearly evident, electrodes i1 and 18 extend inwardly into the space enclosed by the casing.

' While shown as parallel, their relative'disposia potentiometer electrode does not havesubstantially all of the potential gradients passing through it between the spaced electrodes that any movement of such apotentiometer electrode will not result in the greatest change of potential since all liquid shunt paths will be unaffected. However, under some conditions it may be desirable to have a potentiometer function in this manner and it is to be clearly understood that the potentiometer electrode may be as large or small as desirable.

In the event thata potentiometer electrode is used having a substantial area as described above, vibration of the electrode between the spaced electrodes, will result in variations of potential. A mechanical system of this order has weak resonance characteristics and very little resistance so long as the movable electrode has practically no surface transverse to the line of motion. Of course, if liquid damping is-desirable then some fins transverse to the line of motion may be provided. 1

The invention will-now be described'in detail in connection with the drawing.

Figure l is a sectional view of a pick-up;

Fig. 2 is a section along 2-2 of=Fig. 1; and

Fig. 3 is a circuit diagram showing how the pick-up may be connected.

While a phonograph pick-up has been illustrated as a specific example, it is clear that in place of the needle a diaphragm may be substituted and thus a microphone maybe had.-

Reierring, to the drawing, a liquid container 7 or casing 10 may be provided. This casing has a bottom H, sides I! and I3, and front and rear ends l4 and IS. The container may be of any suitable material, preferably an insulator not affected by the liquid content. Thus glass, Bakelite, hard rubber or any plastic may be suitable.

End wall I5 has molded or sealed therein a pair of stiff wire electrodes l1 and I8. These electrodes may be of copper, brass, tungsten j or even tion is of no great importance. Preferably they lie in a plane parallel to bottom ll.

The front end of easing ill has a circular aperture 22 in bottom ll. The wall material has its thickness built up there to give a satisfactory supporting surface. Within aperture 22 is is a sealing plug 23 of soft rubber through which passes the vertical part 24 of a vibratable needle assembly.

Part 24 extends upwardly and has an upper portion 25 provided with a threaded tip 26 extending into a suitable well in 24 so that both 24 and 25 may be screwed together. Upper part 25 extends through an aperture 30 in cover plate 3| and has a thrust ring portion 32 adapted to rest on cover plate 39. A bearing cup 33 fits over the extreme upper tipof part 25 to enclose the same. It is understood of course that the various seals are liquid tight. a

Tightly clamped between post portions 24 and 25 is a movable flat electrode 35 preferably lying in the plane determined by electrodes H and i8 and has substantial width in comparison to the distance between electrodes H and I8. There is no exact ratio and the only necessity is to insure the convergence of substantially all potential gradients thereto. Small ears 38 and 31 extoo low a resistance.

an insulating section 39 to which is attached a needle holder 40 for clamping a phonograph needle 4|. A jewel may be permanently fixed insteadif desired. A lead 42 of fine wire is soldered to part 24.

The container is filled with a liquid as described above and cover 3| is sealed in position in any suitable manner. The pick-up may be supported on a tone arm in any desired fashion. One example of a satisfactory liquid is a mixture of octyl and butyl alcohols. The octyl alcohol has too high a resistance while the butyl has A mixture of the two in proportions of one-third butyl and two-thirds octyl operates satisfactorily. With this mixture I have used potentials of about 225 volts and obtained satisfactory pick-up potential changes.

Preferably, the resistance to turning of part 24 is slight. In fact rigid bearings for part 24 may be provided and plug 23 may be designed to furnish sealing with slight resistance to turning movement of part 24. It is clear that some zero position restoring force is necessary but this may be very small. The weight on the needle point is preferably reduced to a low value, just enough to impart movement to electrode 30 and feed the pickup along the spiral groove.

Referring now to Fig. 3, electrode I! may be grounded while electrode I3 is connected through a resistance 50 to any suitable source of direct potential as point 5|. Resistance 50 is for filter purposes and in practicemay have a value of nec osis several hundred thousand ohms. A condenser is connected from electrode it to ground to cornplete filtering.

Pctentiometer electrode 35 is eonnected through a blocking condenser 55 to control grid 6% of a vacuum tube amplifier 5i. (Condenser is merely to isolate the direct current from con trol grid 55?, and may have a value of about .31 mf. to pass audio frequencies. A grid resistor 58 of about 1 megohm (or whatever value amplifler 67 requires) is connected from grid 5*; to ground. Cathode Si is maintained'at a suitable positive potential above ground by bias resistor 82 shunted by a by-pass condenser t; as is customary. As shown here, the amplifier iii has an accelerating anode 64 connected. to pointii while the anode proper 65 is connected to point bl through a resistor 36. Any other amplifier circuit maybe provided.

ed to have a substantial potearea and being separated by a distance in the in comparison to any 'transverw electrode dimension, said elec od being odspt fierenee inn therebettveen to cause a current flow t" ough saidinuld, and a new omelet else trade between said flli'il elect-re" a, said gootem t meter electrode being movable along straight es between sgoaoed said goot ntlometcr electrode having an eiieetive olec e area disposed along lines oonnecting teed electrodes with the area being much tor than the area o3 flrstnamefi eleces, the liquid resistance high enough and said potentiometer electrode area being great enough so potentiome r electrode concen trates substantially all the potential gradients passing through the liquid in itself to create two substantially separate series connected liquid paths.

3. A translating means comprising the potentiometer of claim 1 wherein means are provided tor moving said potentiometer electrode in ac" eordance with mechanical movements to be translated.

3.. A phonograph pick up comprising the potentiometer of claim 1 wherein a reproducing stylus is provided and wherein means are provided for impressing the stylus vibrations upon said potentiometer electrode. v

HENRY M. 

